1. Field of the Invention
One embodiment of the present invention relates to an improvement of a mobile communication system that forms areas, for example, in a micro cell system.
2. Description of the Related Art
Systems in which a mobile communication system forms areas are classified roughly into macro cell systems and micro cell systems. A representative of the former is a so-called cellular phone system, and the radius of each wireless area reaches several kilometers. A Personal Handy-phone System (PHS) adopts the latter system, and the radius of each wireless area is very small and is on the order of no more than several hundred meters,
For the micro cell system, the number of base stations is frequently increased or decreased in response to changes in communication demand in areas. According to such a situation, station installation design is not usually performed in order to establish the base stations. The resulting interference among areas avoids crosstalk by independently coping with it through each base station.
In this kind of system, when handovers (also referred to as handoffs)are performed, areas are switched in accordance with re-calling from mobile terminals. Since handovers occur frequently in the micro cell system, the system may not be able to suitably cope with high-speed movements of mobile terminals, thus posing a problem. Under the present circumstances, however, the performance of handover depends greatly on the performance of the terminal (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-14265). For instance, an enhancement of high-speed movement performance by using such technique in this reference increases mobile terminal costs, and increases the burden on users. In this technique, since it is necessary to specify ranges of communication areas (zones) in advance for implementation of the technique, this technique cannot be applied to a system in which station installation design is not performed.